I have been using Monefy pro[0] android app for past 4 or 5 years to keep track of my expenses. I log in all my expenses and income in appropriate category. The main free version should be enough for most people but the pro version grants the ability to add custom categories. All the data is stored locally and it has the ability to export our expenses as csv to make reports. Also, Optional google drive and dropbox backup support is included.

P.S. I am not associated with this app. I am just a happy customer.

[0] - https://play.google.com/store/apps/details?id=com.monefy.app...